1. Field of the Invention
The present invention relates to a column unit which connects a chair sheet to a base at which a wheel is installed, and more particularly to a column unit which is designed to regulate the height of a chair.
2. Description of the Prior Art
Generally, a known column unit applied to a chair has a structure in which a gas cylinder is installed in the interior of a base tub. A piston rod of the gas cylinder is rotatably installed at a support plate which seals the lower portion of the base tube by using a ball bearing. A piston installed at the end portion of the upper portion of the piston rod is located in the spindle of the gas cylinder. The interior of the spindle is filled with a pressure gas to perform the function of the gas cylinder. Even when the spindle is moved upward and downward along the piston rod, the pressure gas of the spindle is not discharged. The spindle is divided to upper and lower chambers by the piston. Holes are formed in the chambers to be connected by a bypass channel. A control valve and a control pin which controls the opening/closing operation of the valve are installed in the hole formed in the upper chamber. A chair sheet is positioned at the upper portion of the spindle. A chair base to which a wheel is conventionally mounted is installed at the lower portion of the base tube.
The column unit for a chair comprises the base tube and the gas spindle. The spindle of the gas cylinder is moved upward and downward to regulate the height of the chair sheet. When a user presses the control [pin to open the control valve in the state in which the spindle is located at the lowest position, the upper and lower chambers of the spindle are connected through the two holes and the bypass channel and the pressure gas in the spindle pushes the piston towards the lower position of the spindle to raise the spindle along the piston rod. To the contrary, if a force which exceeds the force of the pressure gas is applied from the upper portion of the spindle in the state in which the control pin is pressed, the spindle is moved downward. The user suitably can regulate the operation of the column unit to regulate the height of the chair sheet. The user can feel the cushion when the user is sat on the chair by the effect of the gas cylinder.
If the length of the piston rod is increased to increase the stroke of the spindle, the area by which the spindle and the tube guide makes contact with each other, i.e., the area by which the tube guide supports the spindle becomes smaller. In case a moment is applied to the upper portion of the spindle, the operation of the column unit becomes unstable or the base tube or the tube guide can be damaged by the load of the moment.
In order to settle the above-mentioned problems, a column unit for a chair is disclosed in U.S. Pat. No. 5,377,942. The patent installs a guide sleeve between the base tube and the spindle.
The patent installs a support ring which is moved upward and downward together with the spindle at the lower end portion of the spindle. An annular recess is formed in the interior of the guide sleeve from the lower side thereof to a predetermined height. If the support ring is raised as the spindle is raised and is caught by the upper end portion of the annular recess, the guide sleeve is raised together with the spindle from then. In case the spindle is moved downward to the lower side, the upper end portion of the guide sleeve is caught by another support ring installed in the spindle and is moved downward together with the spindle.
On the other hand, the patent discloses another preferred embodiment in which a guide sleeve is moved upward and downward together with a spindle by using a pulley and a pulley device.
According to the conventional column unit, in case the spindle is reciprocally moved, the frictional force between the outer surface of the spindle and the inner surface of the guide sleeve moves the spindle upward and downward or the frictional force is not sufficiently generated. As a result, in case two support rings installed at a predetermined position of the spindle and the upper end portion of the guide sleeve is raised, the upper end portion of an annular recess formed on the inner side thereof is moved upward and downward.
In case the frictional force is not sufficiently generated, after the support ring is caught at a predetermined position of the guide sleeve, the guide sleeve is moved. Therefore, in order to regulate the height only to the position, the guide sleeve is not raised and the guide sleeve cannot accomplish its function and the noise is generated when the support ring is caught.
Further, according to the conventional column unit, the number of parts is increased and thus the manufacturing cost is increased. And, the tolerances of the tube guide and the guide sleeve is simultaneously managed, and thus the inferiority rate is increased.